The William‐Wehlau Spectropolarimeter: Observing Hot Stars in All Four Stokes Parameters
Open Access
- 1 November 1998
- journal article
- research article
- Published by IOP Publishing in Publications of the Astronomical Society of the Pacific
- Vol. 110 (753), 1356-1369
- https://doi.org/10.1086/316253
Abstract
We introduce a new polarimeter unit, which, mounted at the Cassegrain focus of any telescope and fiber‐connected to a fixed CCD spectrograph, is able to measure all Stokes parameters I, Q, U, and V across spectral lines of bright stellar targets and other point sources in a quasi‐simultaneous manner. Applying standard reduction techniques for linearly and circularly polarized light, we are able to obtain photon noise–limited line polarization. We briefly outline the technical design of the polarimeter unit and the linear algebraic Mueller calculus for obtaining polarization parameters of any point source. In addition, practical limitations of the optical elements are outlined. We present first results obtained with our spectropolarimeter for four bright, hot‐star targets. We confirm previous results for Hα in the bright Be star γ Cas and find linear depolarization features across the emission‐line complex C iii/C iv (5696/5808 Å) of the WR + O binary γ2 Vel. We also find circular line polarization in the strongly magnetic Ap star 53 Cam across its Hα absorption line. No obvious line polarization features are seen across Hα in the variable O star θ1 Ori C above the σ ~ 0.2% instrumental level.This publication has 19 references indexed in Scilit:
- Spectropolarimetric observations of active starsMonthly Notices of the Royal Astronomical Society, 1997
- On the Periodic X-Ray Emission from θ[TSUP]1[/TSUP] Orionis CThe Astrophysical Journal, 1997
- Periodic X-Ray Emission from the O7 V Star θ[TSUP]1[/TSUP] Orionis CThe Astrophysical Journal, 1997
- Spectropolarimetry. 2: Circular polarization optics and techniquesPublications of the Astronomical Society of the Pacific, 1995
- The magnetic field and abundance distribution geometry of the peculiar A star 53 CamelopardalisThe Astrophysical Journal, 1988
- A CCD Spectropolarimeter for the Lick Observatory 3-Meter TelescopePublished by Springer Science and Business Media LLC ,1988
- The magnetic fields of the AP starsThe Astrophysical Journal Supplement Series, 1980
- The surface magnetic field distributions of 53 Camelopardalis and Alpha-2 Canum VenaticorumThe Astrophysical Journal, 1977
- Circular polarization observations of the interstellar magnetic fieldThe Astrophysical Journal, 1976
- On the Accretion of Material by Theta Orionis CThe Astrophysical Journal, 1972